Measurement of the equilibrium factor between radon and its progeny in the underground mining environment

Abstract

In an undisturbed area with little air circulation, the short-lived radon daughters will come into equilibrium with the parent radon, that is, the concentration ( measured in Bq / m3 ) of radon in air will be equal to the concentration of each of the daughters. However, due to removal processes such as ventilation, plate-out of radon daughters on surfaces, and attachment of these daughters on the aerosol, it is unlikely for radon and its daughters to be in equilibrium in the air. This implies that the concentration of radon daughters is usually less than that of radon in a given equilibrium mixture. A quantity that describes the state of disequilibrium between the concentration of radon and that of its daughters in air is called the equilibrium factor or the F factor. The radiological dose associated with a certain level of radon is determined by the daughter mixture in equilibrium with radon. Knowledge about the value of the F factor is therefore important for assessment of radon dose delivered to human species due to inhalation of air contaminated with radon gas, especially in unventilated uranium-bearing underground mines where workers are usually exposed to higher levels of radon. The aim of this study was to calculate the equilibrium factor on different locations in the underground mining environment. This factor was calculated from the measured concentration of radon and that of its short-lived daughters on different locations underground. The measurements of the concentrations were taken using two types of device, namely, scintillation cells and ML98B Radiation Spectrometer for Radon (ML98B RSR). The former were used to measure the concentration of radon and the latter was used to measure the concentrations of the daughters. On every location, the measurements of the scintillation cells and that of the ML98B RSR were taken simultaneously to ensure that the F factor was the same for both instruments. The results obtained indicate that the levels of concentration of radon and that of its short-lived daughters were different on different locations. The measured concentrations were later used to calculate the values of the F factor which also were different on different locations.